class_docstr: An abstract bridge class. A bridge defines how state is passed
  between encoder and decoder.
  
  All logic is contained in the `_create` method, which returns an
  initial state for the decoder.
  
  Args:
    encoder_outputs: A namedtuple that corresponds to the the encoder outputs.
    decoder_state_size: An integer or tuple of integers defining the
      state size of the decoder.
docstr: Runs the bridge function.
  
  Returns:
    An initial decoder_state tensor or tuple of tensors.
docstr_tok: ["Runs","the","bridge","function",".","Returns",":","An","initial","decoder_state","tensor","or","tuple","of","tensors","."]
code: def __call__(self):
      """Runs the bridge function.
  
      Returns:
        An initial decoder_state tensor or tuple of tensors.
      """
      return self._create()
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  from __future__ import unicode_literals
  import abc
  from pydoc import locate
  import six
  import numpy
  import tensorflow
  from tensorflow.python.util import nest
  from seq2seq.configurable import Configurable
label_desc: Use image node_id 2 for calling the Bridge obj's underlying member method code with example usage: obj.__call__() and returns: self